Additive manufacturing techniques and processes generally involve the buildup of one or more materials, e.g., layering, to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including, e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques may be used to fabricate simple or complex components from a wide variety of materials. For example, a freestanding object may be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing is more commonly known as 3D printing. One such process, commonly referred to as Fused Deposition Modeling (FDM), comprises a process of melting a thin layer of a flowable material (e.g., a thermoplastic material), and applying this material in layers to produce a final part. This is commonly accomplished by passing a continuous, thin filament of thermoplastic material through a heated nozzle, which melts the thermoplastic material and applies the material to the structure being printed, building up the structure. The heated material is applied to the existing structure in thin layers, melting and fusing with the existing material to produce a solid finished product.
The filament used in the aforementioned process is generally produced using a plastic extruder, which may be comprised of a specially designed steel screw rotating inside a heated steel barrel. Thermoplastic material in the form of small pellets is introduced into one end of the rotating screw. Friction from the rotating screw, combined with heat from the barrel, softens the plastic, which may be then forced under pressure through a small opening in a die attached to the front of the extruder barrel. This extrudes a string of material, which may be cooled and coiled up for use in the 3D printer.
Melting a thin filament of material in order to 3D print an item may be a slow process, which may only be suitable for producing relatively small items, or a limited number of items. As a result, the melted filament approach to 3D printing may be too slow for the manufacture of large items, or a larger numbers of items. However, 3D printing using molten thermoplastic materials offers advantages for the manufacture of large items or a large number of items.
A common method of additive manufacturing, or 3D printing, generally includes forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying the bead of material in a strata of layers to form a facsimile of an article, and machining the facsimile to produce an end product. Such a process is generally achieved by means of an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the x-, y-, and z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber or other suitable material or combination of materials) to enhance the material's strength.
The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down or otherwise flattened to some extent, and/or leveled to a consistent thickness, preferably by means of a compression roller mechanism. The compression roller may be mounted in or on a rotatable carrier, which may be operable to maintain the roller in an orientation tangential, e.g., perpendicular, to the deposited material (e.g., bead or beads of thermoplastic material). The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness, thus effecting fusion to the previously deposited layer of flowable material. The deposition process may be repeated so that successive layers of flowable material are deposited upon an existing layer to build up and manufacture a desired component structure. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient enough to allow the new layer of material to melt and fuse with a previously deposited layer, thus producing a solid part.
In some instances, the process of 3D-printing a part, which may utilize a large print bead to achieve an accurate final size and shape, may involve a two-step process. This two-step process, commonly referred to as near-net-shape, may begin by printing a part to a size slightly larger than needed, then machining, milling, or routing the part to the final size and shape. The additional time required to trim the part to final size may be compensated for by the faster printing process.
One desirable application for large-scale 3D printed parts is in the fabrication of molds and/or tooling, commonly used to manufacture components from thermoset materials, e.g., fiber reinforced epoxy at elevated temperatures in an autoclave. Such components are often desired in the manufacture of aircraft and aerospace products. Traditional methods of fabricating these tools may be lengthy, complex, cumbersome, and/or expensive. Tools made from a reinforced flowable material (e.g., a fiber reinforced thermoplastic material) capable of withstanding any process temperatures required are desirable. Tools manufactured this way may be manufactured faster and at a lower cost. One example of a thermoplastic material suitable for the aforementioned application is polyphenylene sulfide, (“PPS”).
PPS, along with numerous other fiber-reinforced thermoplastics, although suitable for a high-temperature operating environment, may exhibit other physical characteristics, which may need to be considered in order to be usable for the aforementioned tools and/or molds. For example, PPS expands in physical size as it is heated and contracts again when cooled. Another characteristic of PPS that may further complicate its use is that material printed using a 3D printer may not expand and contract at the same rate in all directions. During the printing process, the reinforcing fibers may tend to align themselves with a direction of polymer flow, which may result in some reinforcing fibers being aligned along the direction of the printed bead of a flowable material (e.g., printed thermoplastic material). As a result, the printed polymer bead may tend to expand and contract at a slower rate in the direction of the reinforcing fibers and at a faster rate in a direction transverse to the bead length. This may be further complicated by the fact that different methods of printing may result in different fiber orientation within the print bead itself, and different parts may be printed using different patterns and orientations of print bead.
In the practice of the aforementioned additive manufacturing processes, some disadvantages have been encountered. Thermoplastic tools and molds may expand and contract with changes in temperature. However, the amount of expansion and contraction may vary in different directions of a printed bead of material. Owing to variations in the print process and variations in the fiber orientation of the print bead(s), it may be difficult to predict the amount of expansion and contraction of a particular printed part (e.g., a tool or a mold) when exposed to temperature variations.